Undesirable and random polymerization of vinyl monomers can occur spontaneously during handling and processing of the monomer. Such detrimental polymerization lowers the amount of useful polymer producable and also causes fouling of the processing equipment involved. Fouling of the processing equipment occurs continuously during the period monomers are being processed in the equipment. The fouling is caused by the gradual buildup of a layer of the undesired polymeric material resulting from the random uncontrolled polymerization of vinyl monomers. As time goes by, fouling continues until finally the point is reached where it becomes necessary to take the equipment out of service for cleaning. Cleaning is expensive and time consuming, consequently methods of preventing fouling, or at least significantly reducing the rate of fouling, are constantly being sought. Also, it is readily apparent that the loss of monomers due to undesired polymerization is economically detrimental because of useless monomer loss.
Accordingly, it has long been recognized that inhibition of polymerization of vinyl monomers is beneficial and the most economical method of preventing or minimizing polymerization is to add chemicals to the monomers being treated which inhibit polymerization. Various chemicals have been employed as polymerization inhibitors.